Play Rendered Animation is all gray
So there might be a number of things that are happening. Firstly, I would just create a folder and set it as the location where it saves all the rendered images. I personally don't like using the temp folder because there might be other stuff in there. Then you need to go to the Video Sequence Editor and select "open" and select all the images you rendered and the play it. 

Here is a Tutorial

The other thing that is unlikely is maybe something is in front of the camera that is hidden to the viewport but isn't hidden in the render check this in the Outliner. If you want to do a test animation to see how things look just lower the settings and samples and then put it together and see how it looks or you can just play the animation in the viewport. Hope this helped, best of luck to you.